/Engine/Source/Runtime/GeometryCore/Public/Util/ElementLinearization.h
FElementLinearizationmaps a potentially-sparse index list into a linear array. Used linearize things like VtxIds of a mesh as a single array and allow bidirectional mapping between array offset and mesh VtxId. Linearized array offset can then be used for things like matrix row indexing when building a Laplacian matrix.
class FElementLinearization
TArray< int32 >
ToIdMap
TArray< int32 >
ToIndexMap